Circuits with relatively low supply voltages often require higher voltages to optimize performance. Micromachined gyroscopes, for example, are one such type of device that often require such higher voltages. More specifically, conventional micromachined gyroscopes typically have a relatively low supply voltage of between about 2.7 to 5.0 volts. As known by those in the art, many types of micromachined gyroscopes use their supply voltages to generate an actuation force that oscillates a mass. When the oscillating mass is rotated, it responds in an expected manner, which is detected and used to calculate rotational data. Without a sufficient actuation force, however, the mass will not oscillate enough to respond appropriately when rotated. Accordingly, micromachined gyroscopes typically use voltage multipliers to provide sufficiently large actuation voltages.
Voltage multipliers also provide a number of other benefits when used in micromachined gyroscopes. For example, to oscillate the mass, the actuation system in a gyroscope may have a large number of actuation fingers that electrostatically interact with corresponding fingers on the mass. The number of actuation fingers required for proper actuation, however, is roughly inversely proportional to the square of the actuation voltage. In other words, more actuation figures are required for lower actuation voltages, while fewer actuation fingers are required for higher actuation voltages. Consistent with one of the goals of micromachined technology, reducing the number of fingers desirably can reduce the overall size of the gyroscope. Accordingly, in micromachined gyroscope applications, it generally is desirable to multiply the supply voltage to a sufficiently high level that reduces the total number of actuation fingers.
Different types of voltage multipliers can be used for these purposes. FIG. 1 schematically shows one type of prior art voltage multiplier that can be used. Specifically, the voltage multiplier in FIG. 1 operates by connecting two capacitors in parallel across the supply voltage during one half cycle (a charging cycle), and then connecting them in series with the supply voltage during the other half cycle (a voltage multiplication cycle). With this scheme, the output voltage can be raised by increasing the number of switching capacitors to N, in which case the output voltage is approximately equal to the product of the input voltage Vin and (N+1). The voltage multiplier in FIG. 1 therefore uses two capacitors to triple the input voltage.
There are times when it is desirable to multiply the supply voltage by a relatively large amount. In such cases, the voltage multiplier of FIG. 1 may require a relatively large number of capacitors. Increasing the number of capacitors, however, increases the overall size of the gyroscope. In fact, it can effectively cancel out the space benefits derived from using fewer actuation fingers. As noted above, such a result is antithetical to the aim of minimizing the size of micromachined gyroscopes.